1. Field of the Invention
The invention relates to a fuzzy control apparatus using a fuzzy inference.
2. Related Background Art
Hitherto, for instance, a PID control shown in FIG. 2 is used to accurately drive a driving object to a target distance by using a motor or the like while keeping a target speed. FIG. 2 will now be described. A driving object is controlled by using a unit driving distance pulse (hereinafter, referred to as an PI pulse) which is generated every predetermined driving distance .DELTA.D and a target distance DS in which a target arrival distance is shown by the number of predetermined driving distances .DELTA.D. As driving state information which is used in the PID control, the following two data are used: remained distance data Z which is generated from a remained distance calculation circuit 1 for executing a calculation such as to subtract "1" from the target distance DS every generation of the PI pulse and reciprocal data 1/V of a speed which is generated from a speed calculation circuit 2 to count a generation time interval of the PI pulses by clocks (it is more accurate when a clock period is narrower). A PID control circuit section 3 will now be described. The PID control circuit section 3 comprises: a target speed pattern (or function) generating section 4, a proportional state discrimination section 5, a differential state discrimination section 6, and an integration state discrimination section 7. FIG. 3 shows a target speed pattern whose speed is determined by the remained distance. The target speed pattern is supplied to the proportional state discrimination section 5. The proportional state discrimination section 5 calculates V.sub.x /V.sub.r from the remained distance data Z and the reciprocal data 1/V of the speed and the target speed pattern in order to make actual speed data V.sub.x and target speed V.sub.r proportional to a remained distance value Z.sub.x. On the basis of the value of V.sub.x /V.sub.r, the state of speed is classified into five ranks: for example, "very fast", "fast", "indefinite", "slow", and "very slow". The proportional state discrimination section 5 generates driving control data with respect to each of the above five cases. It is a general way to decide the value of the driving control data to a positive or negative value while setting the rank of "indefinite" into "0". A "threshold value" among the ranks and the driving control data are set to constants, respectively. The driving control data is supplied to the integration state discrimination section 7. The integration state discrimination section 7 discriminates the number m of same values (same states) among the driving control data values as a state result which is discriminated from the result of the proportional state discrimination section and properly integrates and discriminates the driving control data and transmits the integration discrimination result to a driving circuit 8 to drive the motor. The driving control data which is generated here is set to a deviation amount for the preceding value (when the remained distance value is larger by "1"). The driving circuit 8 forms drive information for the motor. When the remained distance data is equal to "1", a brake flag is generated and the drive information is set into a braking state, thereby stopping the motor. It is desirable to set the stop position within a range of 0&lt;Z&lt;1. The drive information is sent to the differential state discrimination section 6. On the basis of the deviation amount from the preceding drive information value, a differential state of the speed is discriminated to see if it is in either one of the accelerating state, indefinite state, and decelerating state. On the basis of the result of the discrimination, the integration discrimination amount m is changed. The integration discrimination will now be described in more detail. When the integration discrimination amount is equal to or less than the constant m or when the output of the differential state discrimination section indicates "indefinite", the driving control data as an output of the proportional state discrimination section 5 is allowed to pass as it is. In the other cases, the driving control data is shifted by a certain predetermined amount. It is better to set the shifting direction into the plus direction during the deceleration and into the minus direction during the acceleration. The integration state discrimination section and the differential state discrimination section are needed to reduce a ringing ripple in the speed.
FIGS. 4 and 5 show driving speed patterns for the remained distance value to show the problem of the PID control which has been described above.
The speed pattern shown by a bold solid line of (i) in FIG. 4 indicates the result obtained in the case where the proportional discrimination, integration discrimination, and differential discrimination are set in the PID control in order to reduce an over-amount of the ringing or the like and the control is executed to a usual load. Since the proportional discrimination is optimistic, the speed is largely deviated from the target speed pattern in, particularly, a high speed zone (Z&gt;D.sub.1) and a decelerating zone (D.sub.2 &lt;Z&lt;D.sub.1). Such a "deviation" in the decelerating zone is mainly caused by an inertia load of the driving system and the integration discrimination of the PID control. Therefore, as shown by a broken line (ii) in FIG. 4, not only the "deviation" in the decelerating zone in the over-load state further increases but also the speed just before the stop of the motor is largely "deviated" from the target speed, so that the stop position is deviated to Z&lt;0 in dependence on the braking ability and such a state is unpreferable.
Since the proportional discrimination is optimistic, the motor is not controlled for a small speed fluctuation by a disturbance such as driving load fluctuation, power source voltage fluctuation, or the like, a stationary speed in the high speed zone (&gt;D.sub.1) is not maintained, and an operating efficiency for the driving object is not improved. The above problems are mainly caused since the proportional speed discrimination is optimistic. FIG. 5 shows a driving speed pattern in the case where a sensitivity of the proportional speed discrimination is raised. Although the deviation amounts from the target speed pattern in the high speed zone (Z&gt;D.sub.1) and decelerating zone (D.sub.2 &lt;Z&lt;D.sub.1) are reduced in deed, a ringing occurs in the speed pattern as will be understood from the diagram. Although the ringing in the high speed zone does not cause a large problem, a portion of a very low speed occurs in the low speed zone (Z&gt;D.sub.2) by the ringing. The driving ability of the motor is generally not stable in such a very low speed portion and there is a case where the motor stops. The stop position cannot be guaranteed. Such a setting cannot be performed since it is obvious that the speed ringing exerts an adverse influence on the operating feeling. As mentioned above, the PID driving control has various drawbacks although it is a very simple control. The above problems will now be summarized again.
Problems of the PID control
1) When the state discrimination is enhanced (control is enhanced), a large speed ringing occurs. PA1 2) When the state discrimination is weakened to prevent the speed ringing, a control range is narrowed for environmental changes (driving inertia load, power source voltage). PA1 3) It is difficult to realize a control for a disturbance. PA1 4) The driving control time is not stable for environmental changes.